How much should I charge her?? Am I being unreasonable?

This is why you never do things for family they ALWAYS try to take advantage of you and your aunt is taking horrible advantage; the MINIMUM you should be getting is 10-11 dollars an hour, not one penny less. Stop sitting for her, it isn't worth it and she's a b*tch anyway,. find other people to sit for and make sure you stick to your guns re your pay. Your time has value.